2.80 - use Eevee and Cycles together for motion blur issue
I was able to get this set up by creating a separate scene that composites the Eevee and Cycles scenes together - I have both of those set up with the default composting node setup, but I'm not sure it's required. This allows it to work with all frames, or individual ones if you render from the composited scene.

If it's a sequence, that composited scene clip can then be placed on the timeline in the VSE (in a master VSE scene), but it doesn't have any preview functionality unfortunately, so I set up two tracks - one that contains the original unblurred Eevee clip, so I can edit/render things quickly with the solid shading, and the other has the composited one. I just enable/disable the tracks before exporting. I wish there was a workflow in the compositor for branching off when wireframe/solid is requested, but I haven't seen anything do that yet.

Thanks for detailing your node setup here - it was really useful!